1. Technical Field
This disclosure relates to aircraft radionavigation systems in general, and in particular, to radar augmented landing systems for aircraft.
2. Related Art
The only aircraft all-weather precision landing system currently in use is the well-known Instrument Landing System (ILS), but with the possibility that a Ground Based Augmentation System (GBAS) Landing System, or “GLS,” will be forthcoming in a few years. However, both of these systems are relatively expensive to install and maintain, and in some runway locations, practically difficult to implement.
To make an ILS approach to a runway in bad weather, the weather must be at or above certain specified minimum conditions, depending on the “category” of the ILS system in effect at that runway, i.e., CAT I, CAT II, or CAT IIIa, IIIb or IIIc. If the weather is below the categorization of the ILS, the pilot must revert to a holding pattern, in the hope that the weather will improve to that of the CAT level of the ILS to permit a landing, or divert to another airport to land. Landings may not be made at airports where the environment is below the ILS categorization level.
Systems used by aircraft to make landing approaches can be categorized as either “autonomous” (i.e., systems that rely only on equipment disposed aboard the aircraft, such as an Inertial Navigation System (INS)) and “other-dependent” (i.e., systems that rely on equipment disposed both aboard the aircraft and elsewhere, for example, at the runway, such as an ILS, and/or at another location, e.g., orbiting satellites of the Global Positioning System (GPS)).
In general, there is a need in the industry for systems and methods that can assist in approaching and landing on a runway with such accuracy and integrity that the operation can be considered equivalent to an appropriate ILS “category”, using only equipment on board the aircraft. This would enable the provision of all-weather landing guidance at almost any location (i.e., with no terrain limitations), and at minimal investment in equipment and maintenance costs to airport operators.